In a fabrication process of semiconductor devices such as IC and LSI, microprocessing by lithography using a photoresist composition is carried out. In recent years, with the progress of integration of an integrated circuit, ultrafine pattern formation of sub-micron regions or quarter-micron regions is being required. Following this, there is seen a tendency that the exposure wavelength is shifted to a shorter wavelength side from the g-line to the i-line and further to the KrF excimer laser beams. Further, besides the excimer laser beams, development of lithography using electron beams, X rays or EUV rays is currently advancing.
In particular, the electron beam lithography is positioned as the next-generation or after the next-generation pattern formation technology, and a positive working resist with high sensitivity and high resolution is demanded. Especially, for the sake of shortening the wafer processing time, realization of high sensitivity is a very important problem. However, in positive working resists for electron beams, when realization of high sensitivity is pursued, not only a resolving power lowers, but also deterioration of line edge roughness occurs. Thus, development of resists that can be satisfied with these characteristics at the same time is eagerly demanded. The “line edge roughness” as referred to herein means a phenomenon wherein since an edge of an interface between a pattern of a resist and a substrate irregularly fluctuates in a vertical direction to the line direction due to characteristics of the resist, the edge is seen unevenly when the pattern is seen downward from the upper side. The unevenness is transferred in an etching step using the resist as a mask to deteriorate electrical characteristics, resulting in a lowering in the yield. In particular, in ultrafine regions of not larger than 0.25 μm, the line edge roughness is an extremely important problem to be improved. High sensitivity is in the trade-off relation with high resolution, good pattern shape and good line edge, roughness, and it is very important to satisfy these requirements at the same time.
In addition, in lithography using X rays or EUV rays, it is an important problem to satisfy high sensitivity and high resolution at the same time, and dissolution of this problem is necessary.
As resists that are suited for the lithography process using such electron beams, X rays or EUV rays, chemically amplified resists utilizing acid catalyst reaction are mainly used from the standpoint of high sensitivity. In positive working resists, chemically amplified resist compositions containing a phenolic polymer having such natures that it is insoluble or sparingly soluble in an alkaline aqueous solution and that it becomes soluble in an alkaline aqueous solution by the action of an acid (the phenolic polymer will be abbreviated as “phenolic acid-decomposable resin”, hereinafter) and an acid generator as the major components are effectively used.
With respect to these positive working resists for electron beams, X rays or EUV rays, some resist compositions using a phenolic acid-decomposable resin and a relatively large amount of a compound capable of generating sulfonic acid upon irradiation with active rays or radiations (hereinafter abbreviated as “sulfonic acid generator”) have hitherto been known (for example, see Patent Documents 1 to 5).
However, even in any combination of these materials, it is the present state that high sensitivity, high resolution, good pattern shape, and good line edge roughness cannot be satisfied at the same time in ultrafine regions.
Patent Document 1: JP-A-2002-55457 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)
Patent Document 2: JP-A-2000-66382
Patent Document 3: JP-A-2000-1469
Patent Document 4: JP-A-2001-33970
Patent Document 5: JP-A-11-249292